Magnesita Refractories, a Brazilian company and worldwide leader in refractory and mineral product manufacturing, is a vertically integrated refractory producer supplying to steel, cement, and various other industries. The company is the leading operator in refractory products in South America and serves customers in North America, Europe, and Asia.
One of its plants is a dolomite refractories producer. The process involves mining, sintering, grinding, and finally manufacturing (shaping) bricks. In the sintering process, the plant uses a rotary kiln system which takes milled dolomite and exposes it to prolonged high temperature. Kiln internal temperatures are in excess of 1,600°C. The end product is a densified mineral, which can then be manufactured into various shapes as specified for each application.
The Challenge: Replacing Manual Monitoring
Magnesita has a 300 ft rotary kiln that has been operational for several years. Historically, plant operators would monitor the process -- specifically, the external shell temperature -- by hand, using radiometers and simple methods from which they could determine if the shell needed maintenance or if there was an underlying major structural issue.
This was very inefficient and inaccurate. Readings were not consistently taken on schedule or in the appropriate location, leading to unforeseen shutdowns for refractory repairs and periods of poor quality production due to excessive ring formation. Internal brick fall or product buildup would be nearly impossible to catch before causing a major event.
In 2011, the plant experienced multiple unplanned shut-downs, leading to reduced kiln utilization, increased energy consumption, and unplanned repair and sustainment costs.
Several methods to monitor kiln shell operations were available, including infrared scanning equipment. This would provide detailed, persistent thermal readings of the shell as it rotated and remove the reliance on monitoring by hand.
The Solution: Infrared Scanning
After considering multiple solutions, Magnesita chose HGH Infrared Systems' Kilnscan as the highest performance and best all-inclusive solution to these issues. HGH's infrared scanning system provided the highest resolution and widest field-of-view sensor on the market. Its software platform was easy to use and included functionality that would help Magnesita keep the plant operating for a long time.
The Kilnscan system uses a fast scanning, highly sensitive infrared detector to capture the temperature of the shell, and is able to detect a single brick fall within the kiln. Its ultra-wide field-of-view allowed installation of a single system to monitor the entire 300 ft kiln from a central location, using the existing infrastructure.
In addition to high spatial resolution, the Kilnscan has excellent thermal sensitivity: at less than 1/10 of a degree Celsius, it guarantees sharp and precise display of unwanted change in temperature.
Through a user-friendly 3-D shell display, the Kilnscan provides precise alarms on critical parameters such as hot spots detection, tire slip, or coating loss. High measurement accuracy needs to be consistent over time: by using the internal blackbody to measure and correct a potential slow drift of thermal measurement, the Kilnscan can recalibrate itself when needed, without operator intervention. An external blackbody or the pyrometer are used only for correction of atmospheric absorption in case of bad weather conditions (fog, rain, snow) to ensure the right temperature during these harsh conditions.
Historical data management of all relevant parameters such as temperature profile, brick and coating thickness, kiln speed and tire positions allows the production manager to get, at all times, a clear overview of the kiln status and trends in a centralized dashboard: as a result, kiln maintenance and refractory replacement planning improved.
Last but not least, Kilnscan provides a unique advanced feature. The Thermal Warp Computation allows calculating the thermal distortion induced by temperature changes over the shell to let operators see what's happening within the kiln: evolution of coatings, kiln push of un-burnt material, potential stress on the shell, tires, or roller stations. By collecting and analyzing all the data, the plant manager can get indicators on:
Mechanical and thermal stresses in the shell and tires Hot spots under tires Load fluctuation supported by each pier Shell and tire distortion Breakage of tires according to the fatigue criteria.
With these data in hand, the operator can decrease the shell distortion by adjusting the flame and rotation speed to adapt burning conditions and homogenize the coating. Efficient shell distortion monitoring also results in avoiding hot spots.
Results: Improved Reliability, Utilization
After installation, the process immediately became more efficient. Operators were able to control the proper heating of the kiln and continued plant operation. There were no unscheduled kiln refractory failures and 24/7 operation was possible for just under a year. Operational costs were reduced as no major repairs were needed and production was consistent and predictable.
Control room technicians became more reliant on and trusting of the Kilnscan and human monitoring was unneeded. Regular maintenance was more easily established, freeing up staff to do other things.
Overall, kiln reliability and utilization improved. In fact, a second unit was ordered and installed in 2013.
